Filter elements produced from filter media serve for filtering fluid flows or gaseous media, for example, for filtering an air flow which is supplied to the vehicle cabin of a motor vehicle. Even though it is applicable to any type of filter elements, the present invention and problem to be solved by it will be described in the following in connection with a filter medium or filter element for filtering air for the cabin of a motor vehicle. In the following, such filters are referred to as motor vehicle cabin filters for short.
The increasing air pollution, in particular in big cities, in combination with the use of modern air conditioning systems makes it desirable and also necessary to filter by means of a suitable filter the air that is supplied from the exterior into the cabin of a motor vehicle and that is processed and air-conditioned. For this purpose, for example, particle filters or odor filters or alternatively also combinations thereof are conceivable which are to filter out the particles contained in the air as well as inherent odors from the ambient air as much as possible and to adsorb materials of the ambient air. Such filters for filtering air for the cabin of a motor vehicle are generally known in a plurality of embodiments and variants so that their configuration and function will only be briefly addressed in the following.
Since the efficiency of filters depends in particular on the size of the surface area of the filter that is flowed through by the air, for motor vehicle cabin filters primarily zigzag-shaped folded filter media are used that are also often referred to as pleated filter media. In this way, due to the folding of the employed filter medium, depending on the height of the folds and the fold spacing of the various fold sections of the filter medium, an effective enlargement of the filter surface area flowed through by the air flow can be provided.
As already mentioned, due to the increasing air pollution, increasingly more pollutants are present in the environment of a motor vehicle so that the motor vehicle cabin filter is exposed to an increasing load. These pollutants can be, for example, dust and soot particles as well as pollen, bacterial spores and fungal spores, bacteria and fungi. Some metabolic products of the microorganisms are known to constitute allergic substances for the human respiratory system. In some individuals, they can cause asthma attacks and it is proven that they can cause an immunological defense reaction.
U.S 2003/0 116 2022 A1 describes an air filter for air-conditioning systems as they are used in offices, apartment buildings and buildings for medical services such as hospitals and medical care homes. The filter comprises a composition that contains a biocide that is not bonded to the filter surface but is adapted such that it can migrate through the fine dust that is collecting on the filter so that the pollutant particles are coated with the biocide. Suitable biocides are, for example, 2-bromo-2-nitropropane-1 ,3-diol, isothiazoline compounds, benzoic acid, benzalkonium halides and the like.
U.S. 2006/0021302 A1 discloses an antimicrobial air filter whose filtration medium contains a “prophylactic” compound that can be used to reduce the number of microbial organisms. The “prophylactic” compound is introduced as a separate layer adjacent to the pleated filter medium. The “prophylactic” compound may be water-soluble coenzymes, oil-soluble coenzymes, plant extracts, antibiotics, biocidal metals, aliphatic and aromatic fatty acids, and the like.
WO 2006/003515 A1 discloses an air treatment device for a particle filter of an air conditioning device of a motor vehicle. The device is comprised of a permeable container that contains a volatile treatment agent. The container is attached to the particle filter.
U.S. 2005/0079379 A1 discloses a cover fabric with at least one fabric web that comprises an electrostatically charged meltblown fiber nonwoven nap that is treated with a fluorine chemical with a weak cationic emulsifying agent in order to reduce the surface energy of the fibers to thereby minimize penetration and wetting by oily mists and maintain thereby the effect of the electrostatic charges imparted to the fibers. The fibers can contain polyvinyl-N-pyridinium bromide. The fabric is used for face masks and protective clothing. Use in vehicle cabin filters is not proposed.
Finally, EP 1 882 511 A1 discloses a filter medium with bactericidal effect in particular for filtering air for the cabin of motor vehicles, comprised of at least one filter layer in which contaminants are retainable and a bactericidal filter layer which is downstream of this filter layer and is arranged on the clean air side of the at least one filter layer and is spaced by a spacer layer from the at least one filter layer.
A disadvantage of the solutions disclosed in the prior art is, on the one hand, that they cannot be applied easily to motor vehicle cabin filters and, on the other hand, that they cannot effectively prevent growth of microorganisms on the filter medium and in particular cannot prevent penetration of growth. Moreover, growth, in particular of fungi or fungal spores, is not prevented or only prevented to a minimal extent by the disclosed solutions. Some of the disclosed biocidal agents show an effectiveness only against certain microorganisms, for example, bacteria, but not against molds; for others, an effective inhibition of microbial growth is not ensured by the application of the biocides and the construction of the filter medium.